1. Field of the Invention
The present invention relates to a light emitting device including an LED chip mounted on e.g. a printed wiring board and packaged in a lens member made of a synthetic resin, while also relating to a method of making such a device.
2. Description of the Related Arts
A typical light emitting device of the above-described type includes a pair of first patterned electrode and second patterned electrode formed on an upper surface of a wiring board. On the upper surface of the second patterned electrode is mounted an LED chip, which is electrically connected to the first patterned electrode by wire bonding using a thin metal wire. A lens member made of a transparent synthetic resin is formed on the upper surface of the wiring board at the portion where the LED chip is mounted to package the LED chip and the metal wire.
FIGS. 10 and 11 show a structure disclosed in JP-A 4-28269 as a prior art device. Specifically, a second patterned electrode 2 of a metal film is formed into a circular configuration on the upper surface of a wiring board 1, and an LED chip is mounted at the center of the circle. The circular second patterned electrode 2 is formed with a cutout 4 extending radially inward from the circumference of the circle toward the LED chip 3. A first patterned electrode 5 of a metal film is formed on the upper surface of the wiring board 1 to extend radially outward from a portion within the cutout 4. The inner end of the first patterned electrode 5 is electrically connected to the LED chip 3 by wire bonding using a thin metal wire 6. On the upper surface of the second patterned electrode 2 is provided a lens member 7 formed by dropping an appropriate amount of transparent synthetic resin in a liquid state onto the second patterned electrode for bulging the resin into a hemispherical configuration and then hardening the resin.
In the prior art structure, since the lens member 7 is provided on the second patterned electrode 2 in the form of a circular metal film, the circular second patterned electrode 2 serves as a reflection film of the light emitted from the LED chip 3, whereby the brightness of the emitted light is enhanced.
However, the following problem is caused by the provision of the cutout 4 extending from the circumference of the second patterned electrode 2 toward the LED chip 3 and the provision of the first patterned electrode 5 of the metal film in the cutout 4 to extend radially outward.
When the transparent synthetic resin for forming the lens member 7 is dropped, in a liquid state, onto the upper surface of the circular second patterned electrode 2, the transparent synthetic resin spreads radially outward over the circular second patterned electrode 2 to reach the outer circumference of the second patterned electrode 2 and bulges into a generally hemispherical configuration on the second patterned electrode due to the surface tension. In this state, the synthetic resin is hardened to become the lens member 7.
However, since the outer circumference of the second patterned electrode 2 is interrupted at the portion formed with the cutout 4, and the first patterned electrode 5 is provided at the cutout 4 to project outward, part of the transparent synthetic resin dropped in a liquid state onto the second patterned electrode 2 spreads through the cutout 4, i.e. along the upper surface of the first patterned electrode 5 to project outward from the outer circumference of the second patterned electrode 2.
As a result, the lens member 7 after the hardening does not become a round circle corresponding to the configuration of the second patterned electrode 2 as viewed in plan but becomes an irregular shape partially projecting outward at the portion where the first patterned electrode 5 is provided. Further, the configuration cannot be made generally uniform with respect to a plurality of lens members 7, and the variation of the configuration of the lens members is large.
Conventionally, to solve the above problem, a dam ring 8 surrounding the LED chip 3 and the metal wire 6 is provided on the upper surface of the circular second patterned electrode 2, as shown in FIG. 12. By dropping the transparent synthetic resin in a liquid state into the dam ring 8, the lens member 7 having a predetermined configuration can be formed, and the variation of the lens configuration can be reduced.
However, the provision of the dam ring 8 on the circular second patterned electrode 2 increases the manufacturing cost, which may result in the price increase. Further, the dam ring 8 blocks the light emitted from the LED chip 3 to reduce the amount of light.
It is, therefore, an object of the present invention to provide a light emitting device capable of solving the above-described problems and to provide a method of making such a device.